1. Field of the Invention
Cementitious magnesia compositions containing mixtures of magnesium oxide and other magnesium salts, such as magnesium chloride, and having organo-silicon compounds as viscosity reducing additives, are disclosed in copending U.S. application Ser. No. 891,110 filed on even date herewith and incorporated herein by reference. The present invention is directed to cementitious magnesia compositions containing organo-silanol salts as viscosity modifiers.
2. Description of the Prior Art
There is increasing demand for inexpensive, non-polluting molding and casting compounds as substitutes for scarce petroleum-derived molding materials, and for sprayable fire-proof insulating materials to replace carcinogenic asbestos-containing compositions. Widespread use of magnesium oxide (magnesia) cementitious compositions as substitutes in various molding, casting and spraying applications has been limited by the rather high viscosities of the compositions. The aforementioned copending application discloses organo-silicon compounds (organo-silanes) which have proved to be quite useful in reducing viscosities of magnesia compositions. The reduction in viscosity obtained by addition of certain organo-silanes to "high solids" magnesia compositions is advantageous inasmuch as there occurs no appreciable increase in composition volume that typically results from addition of water as a diluent to reduce viscosity, so that shrinkage of the composition upon curing is minimized. Moreover, with the absence of increased amounts of water as a viscosity reducer, the magnesia compositions do not require substantial increases in curing time and are less likely to aid in corrosion of a substrate.
There have been found some disadvantages, however, in use of certain organo-silane compounds having hydrolyzable groups attached to the silicon atom as viscosity reducing agents. For example, a typically useful organo-silane such as .gamma.-aminopropyltriethoxysilane forms ethanol as a hydrolysis product in the presence of water in a magnesia composition. Other silanes having hydrolyzable organic radicals on the silicon atom may generate hydrolyzates which can be toxic, odorous, volatile or otherwise undesirable. Also, the silane can hydrolyze in the presence of a small amount of water to form undesirable and useless hydrolyzates; hence, care must be taken to ensure that the organo-silane is stored in a hermetically sealed container and that water vapor is prevented from entering the container when it is opened to remove a portion of the silane.